Neuromuscular diseases, which represent disorders of the peripheral nerves and muscles, are a common and growing health care concern. The most prevalent neuromuscular disorders are carpal tunnel syndrome (CTS), low back pain caused by spinal root compression (i.e., radiculopathy), and diabetic neuropathy, which is nerve degeneration associated with diabetes. These conditions affect approximately thirty to forty million individuals each year in the United States alone, and have an associated economic cost greater then $100 billion annually. However, despite their extensive impact on individuals and the health care system, the detection and monitoring of such neuromuscular diseases are based on outdated and inaccurate clinical techniques or rely on expensive referrals to a specialist.
In particular, the effective prevention of neuromuscular dysfunction requires early detection and subsequent action. Even experienced physicians find it difficult to diagnose and stage the severity of neuromuscular dysfunction based on symptoms alone. The only objective way to detect many neuromuscular diseases is to measure the transmission of neural signals. The gold standard approach is a formal nerve conduction study by a clinical neurologist, but this procedure has a number of significant disadvantages. First, it requires a highly trained specialist. As a result, it is expensive and generally requires weeks or months to complete. Second, because they are not readily available, formal nerve conduction studies are generally performed late in the episode of care, thus serving a confirmatory role rather than a diagnostic one.
Thus, there is a need for making accurate and robust nerve conduction measurements available to a wide variety of health care personnel in multiple settings, including the clinic, the office, the field, and the workplace (all of which are sometimes collectively referred to as “point-of-care” settings). However, personnel in these environments generally do not have the neurophysiological and neuroanatomical training to perform such studies. In particular, the correct application of nerve conduction studies requires appropriate placement of electrodes for both stimulation of the nerve and detection of the evoked response from the corresponding nerve or muscle. Therefore, in order to provide effective nerve conduction studies in point-of-care settings, it is necessary to simplify and automate the process of correct electrode placement.
The prior art reveals a number of attempts to simplify the assessment of neuromuscular function, such as in diagnosing CTS, and to make such diagnostic measurements available to non-experts. Rosier (U.S. Pat. No. 4,807,643) describes a portable device for measuring nerve conduction velocity in patients. This instrument, however, does not provide any assistance in the correct placement of stimulation and detection electrodes. On the contrary, a skilled operator with a fairly sophisticated knowledge of nerve and muscle anatomy must ensure correct application of the device. Spitz et al. (U.S. Pat. No. 5,215,100) and Lemmen (U.S. Pat. No. 5,327,902) have also attempted to simplify nerve conduction studies. Specifically, they proposed systems that measure nerve conduction parameters between the arm or forearm and the hand, such as would be required for diagnosing CTS. Both systems suffer from several significant disadvantages, however. First, both systems are large, bulky, and constructed from rigid structures that create a supporting fixture for the arm and hand of an adult. This severely limits their portability and increases their cost. Second, these systems are only applicable to specific limbs and are not generally applicable to numerous anatomical sites. Third, these devices require highly trained operators who can make the appropriate adjustments on the apparatus so as to ensure electrode contact with the proper anatomical sites on the arm and hand. In particular, these systems provide no physiological localization of the electrodes, and as a result multiple placements are often required to find the correct electrode location.
There have been some attempts to simplify the process of nerve localization, primarily for the purpose of avoiding nerve damage during surgical procedures. For example, Raymond et al. (U.S. Pat. No. 5,775,331) describes a system for locating a nerve by applying a stimulus to a plurality of stimulation sites (such as the cavernosal nerve), recording a response to the stimulation (such as the tumescence response), and modifying the stimulation site according to an algorithm that utilizes the response. Although this invention is useful in its intended application of nerve preservation during surgery, it could not be used to simplify or automate nerve conduction studies because it does not provide means to locate the evoked response, leaving this difficult task to the operator.
The present invention avoids the aforementioned limitations.